This mod allows you to set a border for each player with /softborder [get|set|add|subtract]. The borders are kept per dimension and make the player's time more difficult if out of it, depending on how far away they are from their border in that dimension. These effects include:
Increased damage taken, scaling with distance and capped at 150%
Decreased damage dealt, scaling with distance and capped at 50%
Reduced healing, scaling with distance and capped at 50%
The initial range, percentage increase for distance from border, and cap of these effects are configurable. It is also possible to give potion effects at different distances from the origin (or nearest active beacon) in the server config.
Staying near an active beacon has the same effects as remaining within the border; this can be turned off if desired.
Lastly, a vignette similar to the one given for remaining outside a world border will be rendered if the player is out of the safe area. This vignette can be customized by a resource pack that overrides assets/softborder/textures/vignette.png. After drawing the vignette, invert its colors to get it to show up correctly, as it is a color mask rather than an overlay.
This was primarily written for Order of All Creation: Relic Hunters. Potential use cases include to create "sanctuaries" in a post-nuclear wasteland map or growing the border with advancements and quests in an adventure pack. The icon was taken from Lorc's https://game-icons.net/